UI Additions are used to bind a specific behaviour to dom elements marked with a specific selector.
The autosize addition for example is bound to all textareas with an .autosize class attribute and enables an automatic resize of the textarea.

By default the document body will be parsed for additions within the humhub initialization phase. If you require to apply additions to nodes inserted after the initialization phase e.g. nodes loaded by ajax, you'll either have to call the applyTo() function on your new nodes as